UPPER PALAEOZOIC FAUNAS 165 



still surviving, also collapsed in Permian times. 

 Leptaena occurs in the Lower Carboniferous with 

 characters hardly altered from those of Silurian species, 

 while other types of that group (e.g. Davidsonia) assumed 

 the " Neotrematous " habit of complete sessility with 

 atrophy of the pedicle. Orthotetes, an ally of Stropho- 

 mena which is not uncommon in the Carboniferous 

 Limestone, shows similar tendencies. The first members 

 of the surviving group of Thecidiidae made their appear- 

 ance in the Carboniferous, and were usually much larger 

 than their descendants. The family Productidae far 

 excels in importance all other Upper Palaeozoic Pro- 

 tremata. Chonetes, its simplest expression, ranges from 

 the Silurian to the Permian. True Productids appeared 

 in the Devonian, and are almost the commonest of 

 Carboniferous marine fossils. Profuse development of 

 spines, attainment of gigantic proportions, and pro- 

 gressive loss of pedicle-function show that Productus 

 (PI. xi. fig. 6) is, in some ways, a phylogerontic stock 

 among Protremata. Cementation, either by spinous 

 outgrowths or actual " Neotrematous " adhesion, became 

 more and more typical as the group passed through the 

 Carboniferous to the Permian ; it culminated in the 

 extraordinary Hippurites-\\\it Richthofenia of the latter 

 period. Pentameracea lingered through the Upper 

 Palaeozoic, being represented by such small and 

 specialized types as Camarophoria in the Carboniferous 

 and Permian. In that period they disappeared. 



Telotremata showed well-defined members of all three 

 sections in the Devonian. The Rhynchonellids had 

 increased far beyond their Silurian quality, Pugnax 

 (Pl.^xi. fig. 7), Hypothyridina and Allorhynchus being 

 particularly abundant in the Carboniferous Limestone. 

 Terebratulacea with short loops appeared for the first 

 time in the Devonian. These Terebratuloida branched 



